Unitary ambiguity of NN contact interactions and the 3N force

TL;DR

This paper reveals a redundancy in chiral effective field theory between two- and three-nucleon contact interactions, suggesting increased flexibility in modeling three-nucleon systems at high orders.

Contribution

It identifies a specific redundancy in the contact interactions at fourth and fifth order, enhancing the understanding of their interplay in chiral EFT.

Findings

Tensor and spin-orbit three-nucleon contacts account for momentum-dependent two-nucleon interactions.

Redundancy allows better modeling of A=3 scattering observables at N3LO.

Potential for improved accuracy in few-nucleon calculations.

Abstract

We identify a redundancy between two- and three-nucleon contact interactions at the fourth and fifth order of the chiral expansion respectively. In particular we show that tensor-type and spin-orbit three-nucleon contact interactions effectively account for that part of the two-nucleon interaction which depends on the total center-of-mass momentum and is unconstrained by relativity. This might give the chiral effective field theory enough flexibility to successfully address $A=3$ scattering observables already at N3LO.